Potterton Puma 80- HW fine but CH cuts off very quickly

[PeteFilcek]

There have been a few similar posts on the Puma 80 but nothing really answered my problems.

The Hot Water seems to be fine but when the Central Heating kicks in the burners ignite as usual then I hear a knocking noise within the boiler and the burners cut out. A few seconds later the pilot light goes out.

When I ignite the pilot light it is very reluctant to light- this may just be it's age. Once lit, it stays alight with no problems until the CH turns on and then it follows the description above.

The noise has made me think of air trapped in some way?
The other thing to mention is that the HW is extremely hot even when the dial is set to it's lowest setting- could there be a thermostat or automatic cut-out at work?

Any help is appreciated - it's getting cold in the flat again!

 

[kevplumb]

do you have a dripping tap

 

[ChrisR]

PUMP.

 

[corgiman]

bet the diverter valve has gone the way of all things gawd rest it

 

[Agile]

I dont know about the diverter yet but until the pump is sorted we cannot test the diverter.

There can be multiple faults on boilers which have never been serviced.

Tony

 

[baxpoti]

When I ignite the pilot light it is very reluctant to light

Useless tip No.103.....
Turn the electrics to the boiler off, when trying to re-establish the pilot, this stops the fan running.

Useless tip No.1....
Get the boiler serviced regularly

 

[ACOperson]

If changing pump I'd reccomend changing diverter too, I've been to a few and changed one or other, only to find that a few weeks later that the other has failed!

 

[PeteFilcek]

I don't have any dripping taps - I know that could keep the HW firing and not allow the CH to work.
When I relight the pilot everything seems fine with nothing firing. When I use the HW the burners fire on demand as usual and stop once I've finished. It's just the CH that cuts out within seconds and somehow turns the pilot off too.

Some else suggested the thermocouple - any thoughts on that?

The consensus seems to be that it's the pump and diverter valve - would this allow the CH to start firing but then cut out quickly?

Next question - is this a job for a pro or can a competent amateur do the replacement?

 

[baxpoti]

PUMP.

Pump

 

[ACOperson]

I'm sure the Puma has a TC interrupter, so could cut out pilot if overheated.

Maybe one of the Potterton guys could confirm this but I think its right.

Thermocouple should maybe be changed anyway if its a few years old. also check the pilot assembly for blockages.

The problem you are describing sounds like:

-boiler senses hot water demand
-fires, but pump does not turn
-dhw is heated thru 4 pipe HE, but primary water remains still and begins to overheat
- dhw flow alone thru HE does not take up sufficient heat to prevent full overheating-
- Boiler overheats, Tc interrupter cuts out pilot.

Change the pump, but I really advise to change diverter too, they have a wax element which does not like repeated overheating, and are unreliable at the best of times.

 

[Slugbabydotcom]

Well my starting point would be the thermistor IF the pump sounded ok AND there was no problem with the downstairs rads not getting hot.

 

[ChrisR]

Pete
With boiler off, undo the octagonal knob on the pump and pull it towards you a bit. (Dribbles). It should be possible to engage the rotor and turn it. You can feel it because it's weighty.
With the boiler on (HW on) the pump and knob should be spinning if you pull it slightly towards you.

 

[Soggy_weetabix]

Well my starting point would be the thermistor IF the pump sounded ok AND there was no problem with the downstairs rads not getting hot.

Hear hear.

Just got in from one. Even the Potterton Experts could not muster enough brain cells to replace the faulty part.

"PCB mate...their sh*te" my customer was told.
Oh and then..."ill have £260 quid"

God love the ******* at Potterton

Dave

 

[baxpoti]

It's just the CH that cuts out within seconds and somehow turns the pilot off too.

Thermistor? Don't think so

 

[Duzzer]

I'd be looking at Pump and then Divertor valve but you can change the Wax Capsule inside the valve saving you money and time the rest of it is only brass casting and their is a locking nut between two sheets of metal which are a bugger to get undone.Their is usually a 30 sec/2min delay on the valve opening to the CH flow so after the pilot cuts out hold the pipe for a bit to see if the heat leaves the boiler.